Projectile skirt



' J l 19, 1966 A. F- MARDARELLO 3,2 1,290

PROJEC'IILE SKIRT Filed June 5, 1965 m F19 j INVENTOR. ALFRED F.MARDARELLO ATTORNEYS United States Patent 3,261,290 PROJECTILE SKIRTAlfred F. Mardarello, Hoboken, N.J., assignor to the United States ofAmerica as represented by the Secretary of the Army Filed June 3, 1965,Ser. No. 461,208 6 Claims. (Cl. 102-38) The invention described hereinmay be manufactured and used by or for the Government for governmentalpurposes without the payment to me of any royalty thereon.

This invention relates to an improved projectile skirt.

Skirts are attached to the base of a projectile for the purpose ofenhancing the aerodynamic characteristics of the projectile by giving itwhat is commonly known in the art as a boattail effect. Increasedprojectile range with a given payload is thus realized. The skirtcommonly used is a hollow contoured body fitted to the projectile toform a smooth streamlined missile. The high drag forces ordinarilyindigenous to a flat base projectile are considerably reduced as aresult of this streamlined configuration. This diminished drag eifectmakes the aforesaid increased range possible.

A projectile-skirt combination is ordinarily incorporated into astandard cartridge containing a propellant and primer therefor. Thepropellant surrounds the skirt and also fills the hollow cavity thereof.When the cartridge is suitably fired the propellant gases develop thehigh pressure necessary for launching the projectile. The interior ofthe skirt is materially subjected to the high pressures While theprojectile traverses and exits the launcher barrel. Accordingly theskirt must be carefully designed to withstand these pressures, otherwisethe skirt might rupture resulting in serious consequences. Due to thehigh pressure to which the skitrs are subjected they are looked upon aspressure vessels with design factors governed accordingly. By thiscriterion the skirt is designed as a hollow shell with a uniforminternal pressure. As those skilled in the pressure vessel art readilyunderstand, this necessitates a thick walled heavy skirt. Additionalweight is naturally given to the projectile. Since weight of projectileis a limiting factor in its design the weight of a given skirt is,likewise, limited. The added skirt weight shifts the center of gravityof the projectile toward its rear. The effect of this center of gravityshift is critical in that the projectile can become unstable in flightif the shift is too great. Hence the skirt must either be eliminated ormade so short in length as to be virtually unnecessary in light of thesmall increase in range it would provide.

Aerodynamic drag forces are reduced as the length to diameter ratio ofthe projectile is increased. As noted above, the weight of a skirt whichmay be used with a given projectile depends upon the internal pressureit must withstand and the center of gravity shift which it imparts tothe projectile. Since the length of the skirt is also dependent upon itsweight it, of course, follows that the length to diameter ratio of anyprojectile-skirt combination is likewise dependent upon skirt weight.

In the above illustrations the payload weight of the projectile wasconsidered constant. The heavy skirts could be sli htly lengthened ifthe Weight of the payload was reduced. However, this is rarelyconsidered since a relatively greater volume of payload material must beremoved to compensate for addition of a small volume of the much heavierskirt material. The increase of skirt length available by this approachcould only provide a small increase of range while considerably reducingthe payload effectiveness.

In summary, the existing projectile skirts are seriously limited intheir applications and, for all practicable purposes, a projectiledesigner has only two alternatives when considering whether or not touse a projectile-skirt combinationhe may select a heavy, short skirtsufficiently strong to withstand the internal gas pressures; or he mayuse no skirt at all. The heavy, short skirt unduly optimizes the lengthdiameter ratio available with any given projectile while seriouslyaffecting payload weight. On the other hand eliminating the skirtaltogether necessarily means that the range available to a givenprojectile is limited by the increased drag force effects on thatprojectile.

Accordingly, it is an object of the present invention to provide aprojectile skirt which is lightweight and able to withstand the internalpressures engendered by burning propellant gases.

-It is a further object of the present invention to provide a projectileskirt which can be formed from material the same as or different fromthat of the projectile to which it will be attached.

It is still another object of the present invention to pro vide aprojectile skirt which can be manufactured as a separate element orintegrally formed with a projectile.

It is yet another object of the present invention to provide aprojectile skirt which is thin Walled and lightweight and contains aplurality of longitudinally formed openings therethrough which openingsallow a rapid release of propellant gases from the skirt cavity therebyresulting in pressure equalization on both sides of the skirt wall whenthe skirt is still within and exiting the launcher barrel.

The foregoing and other objects and advantages will become apparent fromthe following detailed description thereof, consideration being givenalso to the attached drawings in which:

FIG. 1 is a side elevation view partly fragmented showing an embodimentof the present invention;

FIG. 2 is a perspective view of FIG. 1 showing further details ofconstruction;

FIG. 3 is a view of FIG. 1 showing same in an environmental setting;

FIG. 4 is a perspective view of the present invention showing anotherembodiment thereof.

Referring to the figures wherein like reference numerals refer to likeparts 10 is a hollow skirt which is curvilinear in shape (frusto conicalin this embodiment) having a restricted opening at its rear end. Theskirt 10 is fixed to the rear end or base of a projectile 12. The skirt10 may be secured to the projectile by any suitable means such askeying, threading, pressing, forcing, sweating or the like, so long asthe two elements are rigidly fixed to each other to form a singlecontinuous surface. The skirt 10 may also be formed as an integral partof a projectile 12 as shown in FIG. 4.

The skirt 10 is considerably thin walled with regard to the wall 14 ofthe projectile 12. This necessarily means that the weight of skirt perunit length is considerably less than that of the projectile 12. Thesignificance of the thin walled skirt of this invention will be apparentfrom further reading of this specification.

The skirt 10 is provided with a plurality of openings longitudinallyoriented along the wall of the skirt 10 and passing therethrough. InFIG. 1 the openings are shown as four slots 16 extending from therestricted rear end of the skirt 10 to a point midway along the surfacethereof. The slots 16 are spaced ninety degrees apart in thisembodiment. In FIG. 4 the openings are shown as holes 17, circular inshape and arranged in a regular pattern. The function of the openings ofthe skirt 10 are best understood by considering FIG. 3. In thisillustration the projectile 1'2skirt 10 combination is shownincorporated in a cartridge 18 containing a propellant mix 20 suitablefor a desired application. The cartridge 18 '5 =3 and projectile-skirtarrangement is shown positioned in a launcher barrel 19 illustrated inphantom outline. The cartridge 18 contains a primer 2.2 for firing thepropellant 20. The propellant 20 fills the greater portion of thecartridge 18 cavity and also surrounds the skirt 1i and fills the skirtcavity. When it is desired to fire the projectile l2-skirt the primer 22is initiated igniting the propellant 20. The ignited propellantengenders a typical high pressure front for motivating the projectileout of the launcher. The cavity of the skirt 10 is naturally subjectedto the high pressure while the projectile-skirt combination remains inthe launcher barrel. The slots 16 allow the gases within the cavity ofthe skirt 10 to rapidly escape therethrough thus resulting in anequalization of gas pressure on either side of the skirt wall while theskirt is within and exiting the launcher barrel 19. It is to beunderstood that the gases will also escape through the skirt 10 rearopen end. However, it has been found that an open ended skirt alone isinadequate to allow the entrapped gases to escape rapidly enough toresult in equalization of pressure on both sides of the skirt wall.

The equalization of pressure on both sides of the skirt 10 wall permitsthe skirt 10 to have a wall thickness thinner than was normally usedheretofore. The old art skirt walls had to be strong enough to withstandthe high pressures within the skirt cavity. This naturally meant athicker walled skirt as well as a skirt which was considerably heavierper unit length than is the skirt of the present invention. Theadvantages of the lightweight skirt have been pointed out earlier inthis specification.

The embodiment shown in FIG. 3 shows a payload 24 within the projectile12. The payload 24 may be any well known explosive or other agentsuitable for a particular use. The effect of the old art heavy skirt ona payload has also been pointed out earlier in this specification, alongwith statements showing how a lightweight skirt 10 as that of thisinvention avoids the detrimental elfect on the payload.

The openings through the skirt 10 wall, illustrated as slots 16 andholes 17 in FIG. 2 and FIG. 4 respectively, may take any shape andpattern in accordance with a particular application. The importance inselecting the type opening and the pattern thereof is that a suitablearrangement be selected so that a rapid escape of propellant gases bemanifested in order that the gas pressure he equalized on both sides ofthe skirt 10 wall.

I claim:

1. The combination of a projectile, a propellant, means for firing thepropellant, and a thin walled hollow contoured skirt secured to the rearof said projectile and defining a continuous curvilinear surface withthe outer surface of said projectile, said skirt having a restrictedopened rearward end and a predetermined pattern of openings through theskirt wall to provide an escape for propellant gases whereby pressureequalization on either side of the skirt wall may be effected.

2. The combination as set forth in claim 1 wherein the material of saidprojectile is the same as that of said skirt.

3. The combination as set forth in claim 1 wherein the material of saidprojectile is different from that of the skirt.

4. The combination as set forth in claim 1 wherein said skirt and saidprojectile are distinct from each other and said skirt is locked to saidprojectile by suitable means.

5. The combination as set forth in claim 1 wherein said skirt and saidprojectile are integral.

6. The combination of a projectile having a thick wall of densematerial, a propellant, means for firing said propellant, and a skirtdefining a hollow contoured member having a restricted opened rearwardend and having a wall thinner than said projectile wall, said skirtbeing constructed from a material having a density less than that ofsaid projectile and having a predetermined pattern of openings throughthe skirt wall to provide an escape for propellant gases wherebypressure equalization on either side of the skirt wall may be effected.

References Cited by the Examiner UNITED STATES PATENTS 40,092 9/ 1863Dibble. 1,141,042 5/1915 Davis 102-50 1,274,281 7/1918 Kowalski 102-50 X2,297,130 9/1942 Bomar 102-50 2,433,334 12/1947 Birkeland 102-38 X DBENJAMIN A. BORCHELT, Primary Examiner.

R. F. STAHL, Assistant Examiner.

1. THE COMBINATION OF A PROJECTILE, A PROPELLANT, MEANS FOR FIRING THEPROPELLANT, AND A THIN WALLED HOLLOW CONTOURED SKIRT SECURED TO THE REAROF SAID PROJECTILE AND DEFINING A CONTINUOUS CURVILINEAR SURFACE WITHTHE OUTER SURFACE OF SAID PROJECTILE, SAID SKIRT HAVING A RESTRICTEDOPENED REARWARD END AND A PREDETERMINED PATTERN OF OPENINGS THROUGH THESKIRT WALL TO PROVIDE AN ESCAPE FOR PROPELLANT GASES WHEREBY PRESSUREEQUALIZATION ON EITHER SIDE OF THE SKIRT WALL MAY BE EFFECTED.